1. Field of the Invention
The present invention generally relates to a wireless power transmitter, a wireless power receiver, and control methods thereof, and more particularly, to a wireless power transmitter, a wireless power receiver, and control methods thereof, which can wirelessly transmit/receive charging power.
2. Description of the Related Art
Mobile terminals such as a mobile phone, a Personal Digital Assistant (PDA) and the like are driven by rechargeable batteries, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. In general, separate contact terminals are arranged outside of the charging apparatus and the battery, and the charging apparatus and the battery are electrically connected to each other through contact between the contact terminals.
However, since the contact terminals outwardly protrude in such a contact type charging scheme, the contact terminals are easily contaminated by rogue substances and thus the battery charging may not be correctly performed. Further, the battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Recently, a wireless charging or a non-contact charging technology has been developed and used for electronic devices to solve the above-mentioned problem.
Such a wireless charging technology employs wireless power transmission/reception, and corresponds to, for example, a system in which a battery can be automatically charged if the battery is laid on a charging pad without the need of connecting the mobile phone to a separate charging connector. In general, electronic products are wirelessly charged through the wireless charging technology, and the portability of electronic devices can be increased since there is no need to provide a wired charging apparatus. Therefore, technologies related to the wireless charging technology are expected to be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and an RF/microwave radiation scheme converting electrical energy to microwaves and then transmitting the microwaves.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected all electronic products will be wirelessly charged, anytime and anywhere, without a wire in the near future on the strength of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves.
A power transmission method through electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnet is moved in a coil, an induction current occurs. By using the induction current, a magnetic field is generated at a transferring end, and electric current is induced according to a change of the magnetic field so as to create energy at a reception end. This phenomenon is referred to as magnetic induction, and the electric power transmission method using magnetic induction has a high energy transmission efficiency.
With respect to the resonance scheme, electricity is wirelessly transferred using an electric power transmission principle of the resonance scheme based on a coupled mode theory even if a device to be charged is separated from a charging device by several meters. A wireless charging system employs a concept in physics that resonance is the tendency in which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork oscillates at the same frequency. Similarly, an electromagnetic wave containing electrical energy can be made to resonate, and resonated electrical energy is directly transferred only when there is a receiving device having the resonance frequency present. The remaining electrical energy which is not used is reabsorbed into an electromagnetic field instead of being spread in the air, so that the electrical energy does not affect surrounding machines or people, unlike other electromagnetic waves.
Meanwhile, research on a wireless charging method is currently being conducted, but standards for a wireless charging order, a search for a wireless power transmitting unit/receiving unit, selection of a communication frequency between the wireless power transmitting unit/receiving unit, a wireless power control, selection of a matching circuit, and communication time distribution to each wireless power receiving unit in one charging cycle, and the like, have not yet been proposed. Particularly, there is a need for a standard for a configuration and a procedure in which the wireless power receiving unit selects the wireless power transmitting unit to receive wireless power.
Specifically, there is a need to develop a technology which, when the wireless power transmitting unit has a communication connection with a wireless power receiving unit arranged outside of a charging range, excludes the corresponding wireless power receiving unit.